Neural retinal cell transplantation: Authors’ reply

Abstract

We appreciate the opportunity to reply to the respective comments of Drs. Gouras and Wong on our guest editorial. Dr. Gouras states that, “extensive rat, rabbit, and monkey experimentation” has been done in the area of retinal cell transplantation, and that this work justifies human experimentation at this time. While it is not possible to know exactly which studies Dr. Gouras has in mind, the studies that have been published do not prove that transplanted photoreceptor cells make functional connections with the inner retina. With regard to retinal pigment epithelial cell transplants, as indicated in our editorial, no human counterpart to the RCS rat has yet been discovered, which makes the clinical relevance of the successful transplantation reported by Dr. Gouras in these animals questionable. Indeed, he and his colleagues have transplanted retinal pigment epithelial cells in human patients with age-related macular degeneration with no subsequent improvement in vision.1Algvere P.V. Berglin L. Gouras P. Sheng Y. Transplantation of fetal retinal pigment epithelium in age-related macular degeneration with subfoveal neovascularization.Graefes Arch Clin Exp Ophthalmol. 1994; 232: 707-716Crossref PubMed Scopus (305) Google Scholar As further justification for his work, Dr. Gouras states that “all of the patients who have received retinal cell transplants, including 16 in Sweden,” have suffered no complications following their operations. This is clearly not the case, as at least one patient in India suffered a retinal detachment, as we mentioned in our editorial. Accordingly, the present state of knowledge is insufficient to demonstrate proof of principle. Moreover, the safety of retinal transplantation remains questionable at best. It should be noted that, even if retinal transplant procedures performed in patients do not appear to have harmful sequelae clinically, the results of these procedures at the cellular level may preempt such patients from benefiting from possible future treatments. We therefore restate our position that “much more work is needed in animal models of retinal degeneration before retinal transplantation in humans with photoreceptor cell degenerations can be considered a viable therapeutic alternative.” We are pleased to note that Dr. Wong agrees with us that it is misleading to raise prematurely the expectations of patients with retinal degenerations and their families about the potential merits of neural retinal cell transplantation. Dr. Wong makes the important point that it is the responsibility of the professional community, not only to appreciate the frustrations of patients and their families with respect to finding treatments or cures, but also to manage responsibly their hopes and expectations in this regard. This responsibility is even more important now, when accurate information as well as misinformation can achieve widespread dissemination overnight. We share Dr. Gouras’ and Dr. Wong’s enthusiasm with respect to finding treatments and cures for patients with retinal degenerations. We feel strongly, however, that in the area of retinal cell transplantation, the patients’ interests are best served by considering human studies only after proof of principle and safety are well established in animal models.